using System;
using System.Globalization;
using System.Windows;
using System.Windows.Data;

namespace Columbus.Converters
{
    /// <summary>
    /// Converts object value to visibility based on whether the value is null or not
    /// </summary>
    public class ObjectToVisibilityConverter : IValueConverter
    {
        /// <summary>
        /// Mode of conversion
        /// </summary>
        enum ConversionMode
        {
            /// <summary>
            /// Returns 'Collapsed' if null is passed
            /// </summary>
            // ReSharper disable UnusedMember.Local
            // Supposed to be used from calling code
            NullMeansCollapsed,
            // ReSharper restore UnusedMember.Local

            /// <summary>
            /// Returns 'Collapsed' if not null value is passed
            /// </summary>
            NotNullMeansCollapsed
        }

        /// <summary>
        /// Modifies the source data before passing it to the target for display in the UI.
        /// </summary>
        /// <param name="value">The source data being passed to the target.</param>
        /// <param name="targetType">The <see cref="T:System.Type"/> of data expected by the target dependency property.</param>
        /// <param name="parameter">An optional parameter to be used in the converter logic.</param>
        /// <param name="culture">The culture of the conversion.</param>
        /// <returns>
        /// The value to be passed to the target dependency property.
        /// </returns>
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            var collapse = value == null;
            if (parameter != null)
            {
                var direction = (ConversionMode)Enum.Parse(typeof(ConversionMode), (string)parameter, true);

                if (direction == ConversionMode.NotNullMeansCollapsed)
                {
                    collapse = !collapse;
                }
            }
            return collapse ? Visibility.Collapsed : Visibility.Visible;
        }

        /// <summary>
        /// Modifies the target data before passing it to the source object.  This method is called only in <see cref="F:System.Windows.Data.BindingMode.TwoWay"/> bindings.
        /// </summary>
        /// <param name="value">The target data being passed to the source.</param>
        /// <param name="targetType">The <see cref="T:System.Type"/> of data expected by the source object.</param>
        /// <param name="parameter">An optional parameter to be used in the converter logic.</param>
        /// <param name="culture">The culture of the conversion.</param>
        /// <returns>
        /// The value to be passed to the source object.
        /// </returns>
        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotSupportedException();
        }
    }
}